(1) Field of the Invention
The present invention relates to a spray gun, and more particularly, to a nozzle assembly for a spray gun and the nozzle assembly ensures the back board to be biased onto the splitting head.
(2) Description of the Prior Art
A conventional spray gun 100 for spraying paint or the like is disclosed in U.S. Pat. No. 5,217,168 and shown in FIGS. 1 to 3, which includes an air cap 12 and a back board 13 located in front of the nozzle 11, and the air cap 12 and the back board 13 are positioned by a locking member 14 which is threadedly connected to the spray gun 100. The air cap 12 includes a central passage 121 and multiple shape passages 122 and air passages 123. The back board 13 includes cross-shaped holes 131 through which the paint is ejected therefrom. The air cap 12 can be rotated to allow the air to pass through the air passage 123 and to stock the air to pass through the shape passage 122 to form a circular atomized spray, or to block the air passing through the air passage 123 to form a stream spray.
In order to allow the air cap 12 to rotate, a small gap 15 has to be maintained for the air cap 12 and when operating the spray gun 100, the air pressure pushes the air cap 12 and the back board 13 toward the front end of the spray gun 100, so that the back board 13 will contact the back of the air cap 12. However, the nozzle 11, the air cap 12 and the back board 13 have to be cleaned regularly, and when they are assembled to the spray gun 100, the locking member 14 might not be positioned properly and this results in a large gap formed between the air cap 12 and the back board 13. The relative positions between the air cap 12 and the back board 13 may not be correctly set. These installation problems reduces the back pressure when the back board 13 contacts the air cap 12 and increases the power loss to the electric motor and generates high temperature.
The cross shaped holes 131 are in communication with each other so that when the air cap 12 and the back board 13 are not correctly set, the air passes through all of the central passage 121, the shape passages 122 and the air passages 123. The center and the four distal ends of the cross-shaped holes 131 are not independently operated.
When operating the spray gun 100, the back board 13 contacts the air cap 12 by the wind pressure, and when the spray gun 100 is not operated, there will be no wind pressure and turbulent is generated.
When rotating the air cap 12, the user cannot be acknowledged the angle that the air cap 12 is actually moved, and the user cannot know which of the shape passages 122 or the air passages 123 that the paint goes through. The user then has to try by spraying a small amount of the paint to check that the air cap 12 is correctly rotated.